The main objective of this work is the development of techniques for the incorporation of 5-azacytosine (5-AC) and its reduced analogue 5,6-dihydro-5-azacytosine (DHAC) into specific sites of a synthetic oligonucleotide. The resulting modified oligonucleotides will be studied as specific DNA methylase inhibitors and as probes to study the relationship between DNA methylation and gene expression. A phosphoramidite synthon was synthesized and used in an automated DNA synthesizer to prepare dimers and decamers containing DHAC and 5-AC. Reaction conditions were optimized. An efficient method was developed for the oxidation of DHAC to 5-AC in the oligomers.